The present invention relates to a disk controller and, more particularly, to an optical disk controller for an optical disk having a spirally formed track.
An optical disk is employed as one of the data storage units in an information processing system. An optical disk controller performs a data transfer operation between the disk and a host processor.
The optical disk controller includes in general a buffer memory for temporarily storing write data from the host processor and read data from the disk, a format control unit for converting the write data from the buffer memory into data to be recorded on the disk and the data reproduced from the disk into the read data, and a system controller for responding to commands from the host processor to control the data transfer flow. Further included in the disk controller are a servo controller for controlling the focus and tracking of an optical beam on the disk and a drive controller for ordering, under the control of the system controller, the servo controller to perform a seek operation in which the optical beam moves to a target track and a jump operation in which the optical beam jumps to the adjacent track.
When the system controller receives a data transfer command from the host processor, it requests the seek operation of the drive controller, so that the optical beam moves rapidly to the target track. At a time when a target sector on that track is searched, the format controller starts to operate in a data write mode to record the write data from the buffer memory on the disk and in a data read mode to supply the buffer memory with the read data responsive to the data recorded on the disk. In the data write mode, the write data is transferred from the host processor to the buffer memory, and in the data read mode, the read data is transferred from the buffer memory to the host processor. Thus, the data transfer is executed between the disk and the host processor.
However, sometimes in the data write mode no write data has been transferred to the buffer memory at a time the target sector is searched and that the write data transfer to the buffer memory is suspended. Also in the data read mode, the buffer memory is often filled with the read data which are not transferred to the host processor yet. In such cases, the data read/write operation is of course suspended until the write data arrives in the buffer memory or until the buffer memory has a vacancy for accepting the read data. On the other hand, the disk continues to rotate. Since the track on the disk is formed spirally, therefore, the accessible sector advances in sequence, so that the target sector is not searched again even when the write data is transferred to the buffer memory or the vacancy for the read data is formed in the buffer memory.
Therefore, the format controller informs the system controller of a fact that the data read/write operation is suspended due to the above reason. In response thereto, the system controller requests the jump operation of the drive controller to back the optical beam up by one track. To back the optical beam up is called hereinafter "jump back".
However, this jump back operation is performed after the response time of the system controller and the drive controller has elapsed, resulting in lowering in an access speed. Moreover, the system controller must be designed to handle the request from the format controller, and hence the load thereof is made large.